As known, both conventional printing—using printing silk-screen cylinders or frames—and digital-type printing—using one or more printing nozzle heads—are technologies used for applying inks or paints defining motives, patterns, colorations on sheet materials of different kind, such as for example paper, fabrics, non-woven fabrics, felt, etc.
Fabrics or other fibrous materials having a laminar structure, such as of materials made of non-woven fabric, destined either to traditional and digital printing, may be subjected to a series of fabric preparing steps, before printing, and to one or more fabric finishing steps, after the printing step. In some applications, before the printing process the material to be printed must be accurately prepared so that the surface to be printed is reasonably devoid of impurities, is hydrophilic, is arranged in a plane, the warp and weft thereof have been rectified (in case of fabrics) and it has been suitably stabilized from a dimensional point of view.
After the preparing step, the fibrous material is printed by using, for example, (flat or rotating) silk-screen printing techniques and/or digital printing techniques. After the printing step, the printed material is dried and then is subjected to an ink fixing process typically performed by suitable devices (sometimes referred to as “steam treatment devices” or “steam agers”) in which the printed material is held in a steam environment under suitable pressure and temperature conditions in order to fix the ink to the material fibers. Then, the fabric is washed and dried again.
Fixing ink often requires particular conditions: the presence of water in a vapour state, a suitable thermal level, and minimizing as much as possible the oxygen quantity. These requirements have led to exclude: the use of hot air systems due to their high oxygen concentration, the use of water since is capable of dissolving the printing, and the use of chemical solvents since they are expensive and often toxic and therefore difficult to be disposed of. Therefore, many commercially available steam fixing devices are configured to determine the vapour and temperature conditions necessary for correctly fixing the ink on the fabric.
Two main types of steam treatment devices: discontinuous and continuous, are known. The discontinuous devices provide a treatment chamber adapted to receive a determined quantity of a material, for example a printed fabric, and therefore supplied by steam: all the fabric is kept still in the treatment chamber for a predetermined period of time necessary for fixing the ink. At the end of the treatment, the chamber is discharged and the fabric is withdrawn to be taken to a drying station. While the discontinuous steam treatment devices enable to fix the ink on the fabrics, these however are not devoid of limitations and inconveniences. Particularly, the discontinuous treatment (load batch) makes the process slow and therefore unsuitable for high industrial production rates. It is also noted that repeatedly opening the chamber between one treatment and the following—for discharging the treated fabric and loading a new fabric—makes the process highly expensive from an energy point of view; at each opening of the vaporizer, the vapour and temperature conditions necessary for fixing the ink on the fabric are lost: in order to quickly restore the vaporizer to the required treatment conditions, high power consumption is required. Such conditions, besides further slowing the process, heavily affect operating costs and therefore negatively affect the cost of the resulting treated products.
The continuous devices are provided with a treatment chamber. Inside the chamber the treated material, for example a fabric, is moved at a predetermined speed in order to maintain the printed material in the chamber for a time sufficient to enable the ink fixing process. Particularly, the fabric is introduced into the chamber and abutted on a plurality of elements called “sticks” enabling hanging the fabric in a series of apposed loops: the sticks slowly advance inside the treatment chamber so that the steam can fix the ink on the fabric. Then, the fabric is taken to an outlet station to withdraw the fabric from the sticks and guide it outside the vaporizer.
Illustratively, a type of continuous steam treatment device is, for example, described in German patent application No. DE2419611. The vaporizer exhibits a case in which first and second fixing chambers are defined. In the first chamber, a conveyor belt receives the fabric arriving from outside the case and guides it towards the fixing chamber: the conveyor belt is upwardly sloped so that the fabric can be taken to a top area of the case. Then, the fabrics is caused to fall from the belt onto a series of sticks that receives the fabric and places it according to a series of opposed loops. The sticks are caused to slowly advance inside the second chamber so that the steam can suitably fix the ink.
A different configuration of the continuous device is described in patent publication No. WO2008031763A1: in this case, the vaporizer exhibits, in the treatment chamber, a series of horizontal belts on which the fabric is laid in order to define a plurality of loops: the belts are slowly moved inside the chamber so that the steam can fix the ink on the fabric. Further, the vaporizer has an inlet station admitting to the chamber formed by a sloped conveyor belt which is partially placed outside the chamber (portion receiving the fabric) and partially inside this latter (portion supplying the fabric to the horizontal belts inside the treatment chamber). All the conveyor belts, in other words both the sloped belt operating adjacent the inlet station and the horizontal belt inside the treatment chamber, exhibit a fabric abutment surface having through holes.
The described continuous devices enable quickly treating huge quantities of fabric or of other fibrous material to be treated: the fixing process is quicker than the discontinuous vaporizers and therefore generally less expensive. It is also noted that the housing of the steam chamber remains always substantially closed: in this way, it is possible to hold the chamber fully operative under the desired steam conditions, with substantial power savings with respect to the discontinuous vaporizers that, on the contrary, require continuous “thermal re-shootings” at the end of each treatment.